1. FIELD OF THE INVENTION
This invention relates to non-contact type IC cards durable under the presence of contaminants or dust and, more particularly, to an IC card having an electromagnetic induction interface using coils.
2. DESCRIPTION OF THE RELATED ART
A type of IC card which can be effectively improved by the present invention, i.e., an IC memory card which performs parallel transfer of 8-bit (N=8) data will be described below.
IC memory cards (hereinafter referred to as IC cards) are grouped into (1) a multiple pin type and (2) a noncontact type with respect to the method of connection to terminal units, as described on page 24 of "IC card" edited by Denshi Joho Tsushin Gakkai and published by Ohmsha, Ltd. In the case of multiple pin type cards, data exchange can be performed between the IC card and the terminal by 8-bit or 16-bit parallel data transfer, and data can be read from or written in the card at a high speed of about 200 nsec/byte at present. Non-contact type cards have no contact portions and are therefore free from various problems due to mechanical contacts. Non-contact type cards can be used in a bad operating environment such as a factory automation environment since they can have a completely sealed structure. Non-contact systems are advantageous when used as a means for solving the following problems relating to the connection method for multiple pin type IC cards:
(1) a change in internal data or breakdown of internal ICs caused by static electricity entering through connector terminals,
(2) data error or a transmission/reception disabled state due to terminal contact failure,
(3) failure of connection between the card and the terminal unit due to deformation (spreading) of terminals, and
(4) a need for a large insertion/withdrawal force to an ejection mechanism owing to the existence of many pins.
Light, electromagnetic induction or microwaves may be used as a means for supplying power or effecting transmission/reception in a non-contact manner. For non-contact IC cards presently put to practical use, however, a type of electromagnetic induction system which uses what is ordinarily called a sheet coil is adopted for portability, power consumption and performance of the card.
FIG. 13 is a schematic illustration of internal parts of a conventional sheet coil type IC card in a mounted state. As illustrated, a large sheet coil 2, three small sheet coils 3, a control IC 4, a memory IC 5 and a battery 6 are mounted on a printed circuit board 1. The large sheet coil 2 is a coil for receiving power and clock signals supplied from a terminal unit to the IC card (hereinafter referred to as a "power coil"). The small sheet coil 3 consists of three coils, for example, a data receiving coil 3a, a data transmitting coil 3b, and an instruction signal receiving coil 3c. The sheet coils 2 and 3 are formed in the same manner as the conventional pattern formation on a printed circuit board (not specifically illustrated). The memory IC 5 is an IC for storing data, and the control IC 4 is an IC for controlling reading of data from the memory IC 5 or writing data in the memory IC 5 based on an instruction signal received by the sheet coil 3c. The battery 6 is an internal battery for maintaining the data in the memory IC 5. FIG. 14 is a block diagram of the electrical connection of the IC card shown in FIG. 13. A part of the signal obtained by the power coil 2 is supplied to the control IC 4 through a clock signal line 7 and the part rectified by the rectifier circuit 8 is supplied as DC power 9 to the control IC 4 and the memory IC 5. Two diodes 10 serve to stop DC currents from the rectifier circuit 8 and the battery 6 from reversely flowing to the power source. A received data line 11 serves to deliver received data from the receiving coil 3a to the control IC 4. A transmitted data line 12 serves to deliver transmitted data from the control IC 4 to the transmitting coil 3b. An instruction signal line 13 serves to deliver an instruction signal obtained by the instruction signal receiving coil 3c to the control IC 4. All signal exchanges between the card and the external unit (not shown) to which the card is connected are effected by using serial signals. Data exchange between the control IC 4 and the memory IC 5 is carried out by sending through an 8-bit data bus 14 8-bit parallel data into which the serial data is converted, if the control IC 4 has a parallel/serial data conversion function. Sheet coils (not shown) corresponding to the sheet coils 2 and 3 are provided on the terminal side in positions such as to respectively face the sheet coils on the card side while being maintained close to the same, when the card is connected to the terminal. Currents induced in the sheet coils on the IC card side have differential waveforms. Capacitors having small capacitances (not shown) are connected to the signal lines 7, 11, 12 and 13 shown in FIG. 14 to convert, by integration, the differential waveform induction currents into signals which can be processed or used by the control IC 4. This type of IC card further includes several control signal lines, address lines and the like, which will not be specifically described in detail.
As mentioned above, the conventional sheet coils 2 and 3 shown in FIGS. 13 and 14 are formed in the same manner as printed circuit board patterns. That is, a copper foil is formed on the base by plating, and a resist is applied to portions of the copper foil layer which are to be left, i.e., portions for forming spiral coil conductors, and etching is thereafter performed. After the etching, the resist is removed. The sheet coils thereby formed have small sizes; for example, the power coil 2 has a larger size, a diameter of about 20 mm (the number of turns: about 20), and each of the receiving coil 3a, the transmitting coil 3b and the instruction signal receiving coil 3c has a smaller size, a diameter of about 10 mm (the number of turns: about 5).
The non-contact IC card having this electromagnetic induction system performs serial data transmission as mentioned above. The data transfer rate is 500 kbits/sec (2 .mu.sec/bit), which is higher than the data transfer rates of other non-contact systems. This rate is, in terms of the rate of byte transfer for transferring 8-bit data parallel, about 60 kbytes/sec (16 .mu.sec/byte) which is much lower than 5 m bytes/sec (200 nsec/byte) of the multiple pin type IC cards basically designed for parallel transfer. This non-contact transfer system is therefore unsuitable for data transmission/reception using an IC card having a large capacity of several hundred bytes.
FIG. 15 is an enlarged plan view of one of the sheet coils shown in FIG. 13, FIG. 16(a) is a schematic sectional side view of portions of the IC card and the terminal connected in an aligned state, showing lines of magnetic force when the sheet coils of the IC card and the terminal facing each other are connected by electromagnetic induction coupling, and FIG. 16(b) is a schematic sectional side view showing lines of magnetic force when these sheet coils are electromagnetic-induction coupled in slightly shifted positions. As shown in FIG. 15, pads or lands 20 are provided for electrical connection at the two ends of a coil winding 18. As shown in FIG. 16(a), when the IC card is correctly set on the terminal, almost all lines of magnetic force 26 produced by a sheet coil 22 on the terminal side interlink with a sheet coil 24 provided on the IC card side and facing the sheet coil 22 while being maintained close to the same, a current is induced in the sheet coil 24 in accordance with the Lenz's law, thereby transferring the signal in a non-contact manner. If the IC card is placed on the terminal in a shifted position as shown in FIG. 16(b), only part of the lines of magnetic force 26, e.g., 3/4 of the same interlink with the sheet coil 24, so that the electromotive force induced in the sheet coil 24 is reduced to 3/4, and that the induced current is correspondingly reduced to 3/4. The degree of coupling for data transmission and the reliability of the non-contact system are thereby reduced.
In the electromagnetic induction non-contact IC card thus constructed, the sheet coils for transmitting signals in a non-contact manner occupy a large area on the printed circuit board. The provision of these sheet coils makes it difficult to develop large-capacity IC cards in which many memory ICs are mounted on the printed circuit board. To further increase the data transfer rate, the present serial data transmission system may be replaced with, for example, a parallel data transmission system for transmitting 8-bit data parallel. In such a case, there is a need for a further increase in the number of coils arranged, and it is therefore difficult to construct the card for parallel data transmission. Moreover, the degree of electromagnetic induction coupling is easily reduced by an error in positioning the terminal and the IC card relative to each other, so that the current induced in the opposed sheet coil is changed and cannot be constantly maintained with stability, resulting in deterioration of the reliability of data transmitted between the terminal and the IC card. The conventional non-contact type IC cards exhibit these drawbacks.